From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754494AbcDIRbN (ORCPT ); Sat, 9 Apr 2016 13:31:13 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:36071 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753884AbcDIRbM (ORCPT ); Sat, 9 Apr 2016 13:31:12 -0400 Date: Sat, 9 Apr 2016 13:30:34 -0400 From: Chris Mason To: Mike Galbraith CC: Peter Zijlstra , Ingo Molnar , Matt Fleming , Subject: Re: [PATCH RFC] select_idle_sibling experiments Message-ID: <20160409173034.GA85074@clm-mbp.thefacebook.com> Mail-Followup-To: Chris Mason , Mike Galbraith , Peter Zijlstra , Ingo Molnar , Matt Fleming , linux-kernel@vger.kernel.org References: <20160405180822.tjtyyc3qh4leflfj@floor.thefacebook.com> <1459927644.5612.41.camel@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1459927644.5612.41.camel@suse.de> User-Agent: Mutt/1.5.24 (2015-08-30) X-Originating-IP: [192.168.52.123] X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-04-09_10:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 06, 2016 at 09:27:24AM +0200, Mike Galbraith wrote: > > On Tue, 2016-04-05 at 14:08 -0400, Chris Mason wrote: > > > Now, on to the patch. I pushed some code around and narrowed the > > problem down to select_idle_sibling() We have cores going into and out > > of idle fast enough that even this cut our latencies in half: > > Are you using NO_HZ? If so, you may want to try the attached. [ nohz throttling patch ] I tested the nohz throttle two different ways, first with schbench's pipe simulation, it's easily 8% faster with messages bouncing between cpus. In production it's hard to pick a single number because the benchmarks produce latency curves as the workload scales up in RPS. The benefits range from 2-9% depending on the metric. It's a nice win, and I'd love to see it go in. -chris